Abstract: A method of welding a stud 15 to a base material 14, both made of magnesium or magnesium alloy, comprising; a first step of disposing the stud 15 having a projection 28 at an end portion thereof to have a gap to the base material 14; a second step of lowering the stud 15 rapidly; and a third step of welding the end portion of the stud 15 to the base material 14 by discharging an electric charge stored in a capacitor 11 between the base material 14 and the stud 15, each having an oxide layer destroyed by the rapid lowering of the stud 15, wherein the discharge of the capacitor 11 is carried out by applying a pulse signal having a duration of more than 0.1 seconds to a gate of a thyristor 13 as a signal to start welding, the thyristor 13 serving as a discharge switch of the capacitor 11.